THE SEC61 COMPLEX IS ESSENTIAL FOR THE INSERTION OF PROTEINS INTO THEMEMBRANE OF THE ENDOPLASMIC-RETICULUM

Cross-linking studies have implicated Sec61 alpha as the principal com ponent adjacent to newly synthesised membrane proteins during insertio n into the endoplasmic reticulum, Using proteoliposomes which have bee n reconstituted from purified components of the endoplasmic reticulum [Gorlich, D and Rapoport, T.A., Cell 75 (1993) 615-630] me have found that the Sec61 complex, consisting of three subunits, is essential for the insertion of single-spanning membrane proteins, This is true for signal-anchor proteins of both orientations, and for proteins with a c leavable signal sequence, These results support the view that Sec61 al pha is a major component of the ER translocation site and promotes bot h the insertion of membrane proteins and the translocation of secretor y proteins.